EFFECT OF INITIAL WEIGHT VARIATION ON GROWTH PERFORMANCE OF MONOSEX NILE TILAPIA FINGERLINGS
Mohamed M. Said
Aquaculture Department, Faculty of Fish Resources, Suez University, Suez, Egypt.
|Received 6/ 1/ 2015||
Accepted 15/ 2/ 2015
Nile tilapia fingerlings of 6 weeks old after hatching were individually weighed and manually graded into three experimental groups; small fish (Group S), large fish (Group L), and unsorted fish (Group U). Each experimental group were stocked in three different 2 cubic meter hapas installed in a 2000 m2 pond at a stocking density of 50 fish / m2 for further 14 weeks rearing period. At the end of the experiment, the final body weight and final total length were highest in L group (24.79 g; 10.73 cm) then U group (21.3 g; 10.2 cm) which didn’t differ significantly from S group (20.2 g; 10.16 cm). Final coefficient of variation (CVf) was significantly higher (46.46%) in the U group fish than in the L group which in turn was significantly greater than S group (32.9 & 21.51% respectively). The slope of the growth curve (weight vs. time) in the L group (1.56) was significantly higher than growth curve slopes in both S and U groups (1.33 and 1.39 respectively). Specific growth rate (SGR) was significantly higher in the S group (2.86%) than the (SGR) in the U group (2.46%) which in turn was significantly higher than L group (2.23%).The S group was the best in terms of biomass gain (1788%) and feed conversion ratio (1.77). The Final condition index in L group fish was significantly higher (1.93) than that observed in both S and U groups. Hepatosomatic index (HIS), spleenosomatic index (SSI), and viscerosomtic index (VSI) were all significantly higher in the L group (2.00, 0.13, and 9.2 respectively) than those for S and U groups (1.64, 0.11, and 8.2) and (1.6, 0.09, and 8.10) respectively.
Key words: Nile tilapia, size sorting, growth performance, condition based stress indices.